Mysterious Dark Matter

Gravity: the Great Organizer

According to current theory, minute fluctuations in cosmic background
radiation
detected by NASA's Cosmic Background Explorer (COBE) were all that was
necessary to seed the structures which would later become galaxies, galaxy
clusters, even superclusters. But how did those primordial fluctuations detected by COBE become the
gigantic structures we see today?

The answer lies with gravity, which, by the
time radiation and matter parted ways, had become
the dominant long-range force in the universe. But there must have been
enough
matter to have generated the gravity that could pull together the giant
structures which populate the modern universe.

The Omega Factor

The inflationary hypothesis, when applied to the standard Big Bang model of
cosmology, implies that the average density of the cosmos is very close
to or
exactly matches the critical density required to balance its
expansion.

In other words, Omega
equals one. But when all the visible matter is added
together, the
resulting density is but 5, at most 10 percent of the critical density.
Where,
and what, is the missing matter?

And then there are the relative motions of galaxies, galaxy clusters and
giant
superclusters to reckon with. The speeds at which the Milky Way and our
nearest
neighbor, Andromeda, are rotating demand
some extra, unseen matter--otherwise they would simply fly apart.
Not only that, but our Local Group of galaxies and the Virgo
cluster are hurtling toward some great, unseen "Great
Attractor" at more than one million miles per hour!

For decades, astronomers have tried to explain the stupendous velocities they
observe. The objects in question simply don't contain enough
visible matter to
account for the gravitational forces needed to generate these motions.

Clearly there's more out there than meets the eye. That "something," cosmologists
believe, is dark matter. No one quite knows what it's made of, but it
seems to comprise at least 90 percent of what's out there!